Safety device for air actuated assemblies

ABSTRACT

A safety device for use with two concurrently operable fluid actuated assemblies by means of which one of said assemblies may be operated after the other of said assemblies has been rendered inoperative due to development of a leak in the assembly or the conduit leading thereto. One form of the device for use with pressurized air operated assemblies includes time delay means as part thereof, to prevent actuation of the device by a false signal such as could occur if different sized air cylinders were used on the two brake assemblies. Also, the time delay means prevents the device being actuated by a minor leak in the hose or conduit, which is of not sufficient consequence to prevent the two air actuated assemblies from being operated.

United States Patent Hensley [s41 SAFETY DEVICE FOR AIR ACTUATED ASSEMBLIES [72] Inventor: James R. Hensley, 1325 Nutmeg, Escondido, Calif. 92025 [22] Filed: NOV. 23, 1970 [21 Appl. No.: 91,851

1 Related U.S. Application Data [63] Continuation-impart of Ser. No. 846,443, July 31, 1969, Pill. N0. 3,556,616. r

' [52] 1.1,S.CI. ..303/84 A, 137/118, 137/514, 188/151 A, 200/82 D [51] Int. Cl. ..B60t 15/00, B60t 17/18 [58} Field of Search "303/84 A; 60/545 E; 200/82 D; 188/151 A, 345; 137/118, 103, 514

[S6] References Cited 7 UNITED STATESPATENTS 2,944,856 7/1960 Swanson ..303/84 A 1151 3,658,391 [451 Apr. 25, 1972 3,148,364 9/1964 Engels et ul AX 3,439,139 4/1969 Stelzer ...303/84 A UX 3,556,616 1/1971 Hensley ..303/84 A Primary Examiizer-Milton Buchler Assistant Examiner-John .l. McLaughlin Attorney-William C. Babcock [57] ABSTRACT A safety device for use with two concurrently operable fluid actuated assemblies by means of which one of said assemblies may be operated after the other of said assemblies has been rendered inoperative due to development of a leak in the assembly or the conduit leading thereto. One form of the device for use with pressurized air operated assemblies includes time delay means as part thereof, to prevent actuation of the device by a false signal such as could occur if different sized air cylinders were used on the two brake assemblies. Also, the time delay means prevents the device being actuated by a minor 7 leak in the hose or conduit, which is of not sufficient consequence to prevent the two air actuated assemblies from being operated.

I 7 Claims, 9 Drawing Figures PATENTEDAPR 25 1972 3, 658 391 sum 1 BF 2 INVENTOR.

F|G.5 J JMES RHENSLEY BY YEW a m AQTTOENEY PATENTEDAPR 25 I972 sum 2 [IF 2 FIG.8

Y My 2 w M a ATTORNEY SAFETY DEVICE FOR AIR ACTUATED ASSEMBLIES C ROSS-REFERENCES TO RELATED APPLICATIONS I The present application is a continuation-in-part of my application Ser. No. 846,443 entitled Safety Device For Fluid Actuated Assemblies, filed in the United States Patent Office on July 31, I969 now U.S. Pat. No. 3,556,616.

BACKGROUND OF THE INVENTION l. Field of the Invention A safety device for use with two concurrently operable fluid actuated assemblies, such as automotive brakes or the like to permit operation of one assembly after the other assembly has been rendered inoperative due to the development of a leak therein or in the conduit thereto.

2. Description of the Prior Art In the automotive truck field, air operated brakes are widely used. These brakes are selectively energized in unison by pressurized air from a reservoir mounted on a vehicle. A serious operational disadvantage of air operated brakes is that all of the brakes are rendered inoperative when a substantial leak develops in one of the conduits leading to the brake assembly.

Various safety devices have been designed and used in the past to a limited extent in an attempt to minimize'this hazard, but heretofore they have not proven to be satisfactory, and as a result have not come into widespread use. The present invention solves the above mentioned problem in a simple manner, and eliminates the possibility that a driver of a truck vehicle may find himself without braking power should one of the conduits to abrake assembly fail.

' SUMMARY OF THE INVENTION A safety device in the form of a valve that is interposed between the conduits leading to automotive air actuated brake assemblies and the source of pressurized air that is normally confined in a reservoir carried on the vehicle. Air in the valve of the present invention maintains an equal pressure on opposite sides of a valve member forming a part thereof so long as the brake assemblies and conduits leading thereto are substantially free from leaks. However, in the event that one of the conduits or brake assemblies develops a leak, an unbalanced air pressure condition is immediately set up in the valve, whereby the valve member in the valve body is immediately moved to a position where it prevents further flow of air to the defective conduit or incapacitated brake assembly. After the valve memberhas moved in the valve body as above described, air will flow from the reservoir to the operative brake assemblies to actuate the latter, and hold them in a braking position so long as air pressure is maintained on the valve member.

The safety device includes as an integral part thereof time delay means to prevent the valve member being actuated by. a false signal, such as could occur if the brake assemblies with which the device is associated have air cylinders of different sizes.

A major object of the present invention is to provide an inexpensive safetydevice of simple mechanical structure that may be disposed between a plurality of air actuated assemblies and a source of air under pressure, with the device when so positioned permitting a portion of the assemblies to be actuated after one of the assemblies has been rendered inoperative due either to development of a leak therein, or a leak in a conduit leading to the assembly.

Another object of the invention is to provide a safety device I in which the driver of an automotive vehicle having air actuated brakes retains braking power, even if a portion of the air actuated brakes on his vehicle are rendered inoperative should a leak develp in a conduit leading thereto.

A still further object of the invention is to furnish a safety device that may be easily and quickly adjusted to any desired sensitivity to prevent actuation of said safety device in the event that but a minor air leak occurs in the brake system downstream from the device. 1

Yet another object of the invention is to supply a safety device that is entirely automatic in operation, requires little or no maintenance attention, and can be installed for equally effective results on either new or old automotive vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a form of the safety device particularly adapted for use on automotive vehicles that have air actuated brake assemblies;

FIG. 2 is a longitudinal cross sectional view of a form of air brakes safety device of the structure described and claimed in my copending application Ser. No. 846,433;

FIG. 3 is an enlarged cross sectional view of the form of the safety device shown in FIG. 2, and illustrating the portion thereof within the phantom line in FIG. 2 that is identified by the numeral 3;

' FIG. 4 is a longitudinal cross sectional view of the form of the device illustrated in-FIG. l, and taken on the line 44 thereof, with the device in 'a first non-actuated position;

FIG. 5 is a transverse cross sectional view of the device shown in FIG. 4 taken on the line 5-5 thereof;

FIG. 6 is the same longitudinal cross sectional view as in FIG. 4, but with the valve member in a second position to prevent flow of air through the device to the left as viewed in said figure;

FIG. 7 is a transverse cross sectional view of the device taken on the line 7-7 of FIG. 4;

FIG. 8 is an enlarged fragmentary longitudinal cross sectional view of the device within the phantom lines shown in FIG. 6 that is identified by the numeral 8; and

FIG. 9 is a diagrammatic view of a truck vehicle having air actuated brakes, and-illustrating the means by which both the first and second forms of the safety device may be used thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first form A of the safety device includes a valve body 10, the structural details of which are best seen in FIGS. 2 and 3 inclusive. Body 10 includes an-interior confined space 12 that is in communication with a tapped fluid inlet opening 14, and first and second longitudinally aligned tapped openings 16 and 18 formed in the body.

Body 10 also includes a portion 20 that extends into confined space 12 and is situated between openings 16 and 18. A bore 22 extends longitudinally through body portion 20, and is in axial alignment with openings 16 and 18. First tapped opening 16 is engaged by a first threaded plug 24 in which a longitudinal bore 26-and counterbore 28 are formed, and that at the junction thereof define a circular body shoulder 30. The interior end portion of first plug 24 defines a valve seat 32 that is in communication with bore 26.

Second tapped opening 18 is engaged by a second threaded plug 34 in which a longitudinal bore 36 and counterbore 38 are formed, and at the junction of which bore and counterbore a circular body shoulder 40 is defined. The interior and portion of second plug 34 defines a valve seat 42. The valve seats 32 and 42 both have a number of circular radially spaced serrations 31 formed thereon of transverse V-shaped cross section as may best be seen in FIG. 3. Fluid inlet opening 14 is engaged by a suitable threaded fitting 44 that is connected to a conduit 46 through which fluid under pressure is supplied to confined spaced 12 as shown in FIG. 8. The outer end of first plug 24 is engaged by a conventional fitting 48 that is connected to a first conduit 50, as shown in FIG. 3. Likewise. the outer end of second plug 34 is engaged by a conventional fitting 52 that is connected to a second conduit 54.

An elongate valve member B is slidably mounted in bore 22. Valve member B is preferably formed from nylon or other inert plastic material that does not deteriorate when subjected to hydraulic fluid over a prolonged period of time, and one which will not stick or bind when in contact with the valve portion 20. Valve member B has first and second end surfaces 56 and 58 in which circular recesses 56a and 58a, respectively are formed.

First and second helical springs 60 and 62 are provided, and the ends 600 and 62a thereof engage first and second recesses 56a and 58a, as shown in FIG. 2. The ends 60b and 62b of the springs abut against body shoulders 30 and 40. The springs 60 and 62 tend at all times to maintain valve member B at an intermediate position between valve seats 32 and 42 whereby fluid in confined space 12, or fluid entering said space, is free to flow through valve seat 32 or 42 to the first or second conduits 50 or 54 that are in communication therewith.

The first form A of the safety device is simple to use and install. In FIG. 9 of the accompanying drawings, two of the safety device A are shown installed on a tractor C and trailer D. Both the tractor C and trailer D are provided with first and second sets of rear wheels 64 and 66, and first and second air operated brake assemblies 68 and 70 associated therewith. A tank 72 of compressed air is mounted on tractor C from which a discharge line 74 extends to a normally closed valve 76, and from which valve a header 78 extends. One of the safety devices A is providedfor the tractor C and a second of the devices for the trailer D. Both of the safety devices A are connected to the header 78 by conduits 46.

The first conduit 50 leads from safety device A installed in tractor C to a conduit 80 that extends to brake assemblies 68. The second conduit 54'connected to the safety device A in the tractor C extends to a conduit 82 that proceeds to the brake assemblies 70.

Should a leak develop in the conduits 50, 54, 82 or brake assemblies 68 of the tractor C, fluid discharged under pressure into the safety device A by actuation of valve 76 will flow from the confined space 12 through counterbores 28 and 38 at different rates. This differential in rate of flow from confined space 12 creates a differential in pressure on the first and second end surfaces 56 and 58 of valve member B. The differential in pressure on the end surfaces 56 and 58 causes valve memberB to move to the left as viewed in FIG. 3 and seal with seat 32, due to the serrations 31 pressure engaging one end of the valve member B. The serrations 31 are metal and are of course harder than the plastic material defining the valve member B. When the valve member B is in pressure contact with the serrations 31 a fluid tight seal is effected therewith. The valve member B serves not only this function, but as a sealing member as well, due to the serrations 31 being harder than the plastic defining the valve member. Thus, no resilient O-rings or pads are required to effect a fluid tight seal when the valve member B is in pressure contact with seats 32 or 42. The position of valve member B after completing movement to the left to occupy a sealing position is shown in FIG. 3. Further flow'of air from the confined space 12 to the conduit 50 and brake assemblies 68 is now obstructed, but with the brake assemblies 70 remaining operable.

The sensitivity of the first form A of the safety device in being actuated to obstruct air flow through either conduits 50 or 54 is controlled by the degree of resiliency of springs 60 and 62. If the leak in the conduits 50 or 80, or brake assemblies 68 is of a minor character, the resiliency of springs 60 and 62 will prevent the small differential in pressure on the end surfaces 56 and 58 of valve member B from moving the valve member to a fluid obstruction position. The safety device A on trailer D operates in the same manner as the safety device A above described.

When air is used as the actuating fluid as above described, the valve member B will remain in an obstructing position as shown in FIG 3, so long as the .valve 76 is in an open position. When valve 76 is placed in a closed position, the air in the brake assemblies 68 and 70 by means not shown is vented to the atmosphere, and springs 60 or 62 return valve member B to the non-obstructing position illustrated in FIG. 3. If the brake assemblies 68 and 70 are actuated by hydraulic fluid, the valve member B will remain in a fluid obstructing position. The valve member B- must be returned to the open position shown in FIG. 2 after the leak in the conduits or brake assemblics have been repaired.

Valve member B may be formed from Lexan", a polycarbonate resin manufactured and distributed by the General Electric Company. If desired, valve member B may have a circular recess 84 formed in the center thereof.

The second form of safety device E which is adapted for use with pressurized air only is shown in FIGS. 1 and 4 to 8 inclusive. The second form E of the safety device accomplishes the same results as the first form A thereof, but includes a time delay mechanism that prevents the device assuming an air obstructing position as a result or a false signal. The second form E of the device as may best be seen in FIGS. 1 and 4 includes a hollow valve body that defines an interior hollow space 112. A first tapped air inlet opening 114 is formed in valve body 110 as shown in FIG. 4 and is in engagement with a conventional fitting 144. Fitting 144 is in communication with the conduit 46 that extends to the'header 78 which in turn is connected to the pressurized air control valve 76 as shown in FIG.

The second forms E of the safety device are connected to the tractor C and trailer D in the same manner as the first forms A thereof as illustrated in FIG. 9. Valve body 110 has first and second tapped openings 116 and 118 formed therein. The valve body has a portion 120 thereof that extends into the space 112, with this portion having a bore 122 extending longitudinally therethrough. A first threaded plug 124 is provided as shown in FIG. 4 that has a longitudinal bore 126 therein that is axially aligned with a counterbore 128, with the bore and counterbore at their junction defining a circumferentially extending circular shoulder 130. The inner end of the plug 124 defines a valve seat 132 on which a number of circumferentially spaced serrations 131 are defined.

Second threaded plug 132 is provided that has a bore 136 therein that is axially aligned with a counterbore 138 shown in FIG. 4, and the bore and counterbore at their junction defining a circular body shoulder 140. The second plug 134 on its inner end defines a valve seat 142 on which serrations 131 are defined in the same manner as on the valve seat 132. A threaded fitting 44 is provided that engages the tapped inlet opening 114 and is in communication with the conduit 46 shown in FIG. 9. A tubular fitting 48 of conventional design is threaded or otherwise secured to the first threaded plug 124 and is in communication with the counterbore 128 defined therein. The fitting 48 is connected to conduit 50 as shown in FIG. 9.

A fitting 52 of conventional design is secured to the second plug 134 and is in communication with the counterbore 138 defined therein. The fitting 52 is in communication with conduit 54 as shown in FIG. 9. The bore 122 has a cylindrical valve member F slidably mounted therein, with the valve member having a first end surface 156 in whicha circular recess 156a is formed. The valve member F also has a second end surface 158 that has a second circular recess 158a defined therein. First and second helical springs 160 and 162 are situated within the confines of the bores 126 and 136 as may be seen in FIG. 4, and have first ends 1600 and 162a in abutting contact with resilient flat ring shaped sealing members 163 and 165. The sealing members 163 and 165 are in abutting contact with the recessed ends 156a and 158a.

Valve member F has two longitudinally aligned first and second cylindrical cavities 168 and 170 therein that extend towards one another and are connected by a small diameter passage 172 through which air may bleed. A second small diameter transverse air passage 174 is formed in valve member F and is in communication with first passage 172. The valve member F has a central transverse groove 176 therein that cooperates with the valve body portion 120 to define an annulus shaped confined space 178 as may best be seen in FIG. 4.

First and second circular plates 178 and 180 are positioned in first and second bores 126 and 136 and are held in abutting contact with first'and second body shoulders 130 and 140 by the second ends 16% and 162b of the springs 160 and 162. The springs 160 and 162 at all times tend to hold the valve member F in the centered position in valve body 110 as illustrated in FIG. 4. Y

Circular plates 178 and 180 each have a plurality of circumferentially spaced apertures 182 therein that at allftimes maintain communication between first bore 126 and first counterbore 128 and second bore 136 and second counterbore 138.

First and second plates 178 and 180 have first and second plungers 184 and 186 extending therefrom and towards one another as shown in FIG. 4. First and second plungers 184 and 186 adjacent the free end surfaces 184a and 186a have circumferential grooves 184b and 186b therein that support resilient O-rings 184a and 1860. The plungers 184 and 186 are disposed in first and second cavities 168 and 170, with the rings 1840 and 1860 slidably and sealingly engaging the side walls thereof. The first and second plunger ends 184a and 186a cooperate with first and second cavities 168 and 170 to define first and second confined spaces 188 and 190.

When the second form E of the safety device is being used and a leak develops in one ofthe lines 50, 4, 82 or one of the brake assemblies .68 or 70, the valve member F will be actuated to move to either the right or left in the same manner as valve member B in the first form A of the device. However, when the valve member F is so actuated, there is a short time delay before one of the sealing members 163 or 165 contacts serrations 13, due to the air in one of the confined spaces 188 or 190 being compressed. This compressed air requires a short period of time to bleed from one of the confined spaces 188 or 190 through passages 172 and 174 to a position exteriorly of the valve member F. This above mentioned short period of time required prior to movement of valve member F prevents one of the brake assemblies 68 or 70 being temporarily rendered inoperative as a result of a false signal to the second form of safety device E. It will be particularly noted in the second form E of the device the sealing members 163 and 165 may engage the serrations 131 rather than end portions of the valve member as in the first form B.

The body 110 of the second form E of the safety device preferably has one or more bolt holes 192 extending transversely therethrough to be easily secured to a convenient portion of the tractor C or trailer D by fastening means (not shown).

A tubular internally threaded boss 194 extends outwardly from body 110 and removably supports a normally open pressure sensitive electrical switch 196. The switch 198 is closed when pressure on a face 200 thereof rises above a predetermincd maximum valve. A transverse tapped bore 201 is formed in body 110 and is in communication with'confined space 112 and face 200. A compressed helical spring 202' maintains a ball 204 in sealing engagement with a seat 206; A portion of the ball 204 projects into confined space 112 and within groove 178. g f

When the valve member F moves longitudinally to a closed position as occurs when a leak develops in one of the lines or brake assemblies, a portion 208 of the valve member F contacts the ball 204 to raise it from the seat 206 and allow pressurized air to contact face 200. Switch 198 now assumes a closed position to complete an electric circuit (not shown) through terminals 210, 212 to energize a visual or audible alarm (not shown) to warn the driver (not shown) of the tractor C that he has defective brakes. The spring 202 must be of sufficient strength to 'maintain ball 204 on seat 206 at the air pressure normally supplied to confined space 112.

lclaim:

1, In combination with a pressurized air supply line and first and second air actuated brake assemblies having first and second conduits extending therefrom, a safety device for permitting one of said assemblies to operate when the other thereof has become inoperative by a leak developing therein or in said conduit extending therefrom, said device including:

a. a valve body that defines an interior confined space and first and second axially aligned bores in communication therewith, and a third bore normally disposed to said first and second bores and in communication with said interior confined space, said body including a portion thereof in said interior confined space between said first and second bores, and said portion having a fourth bore therein that is longitudinally aligned with said first and second bores;

b. first and second plugs mounted in said first and second bores, each of said plugshaving a bore and counterbore therein that define a body shoulder at the junction thereof, and said plugs having circular valve seats on the ends thereof disposed in said housing;

' c. first and second apertured plates disposed in said first and second bor'es and in abutting contact with said body shoulders; i d. first and second plungers that are axially aligned and extend towards one another from said plates;

. a single elongate valve member slidably mounted in said fourth bore, said valve member having first and second end surfaces from which first and second cavities extend inwardly towards one another, with said first and second cavities slidably and sealingly engaged by said first and second plungers that cooperate therewith to define first and second confined spaces that are connected to small diameter passage means in said valve body through which air in said first and second confined spaces is bled to the exterior of said valve member;

f. spring means that at all times tend to maintain said valve member in a centered position between said first and second plugs;

g. first and second resilient sealing members mounted on said first and second ends of said valve member;

h. first means for controlling said pressurized air through said supply line;

i. second means for connecting said supply line to said third bore;

j. third means connecting said first and second conduits to said bores and counterbores in said first and second plugs, said spring means so long as there is no substantial leak in one of said brake assemblies or in said first and second conduits maintaining said valve member in a centered position in said interior confined space where pressurized air can flow from said supply line to said conduits, but upon a leak developing in one of said conduits or brake assemblies an unbalanced pressure develops in said interior confined space thatforces said valve member to move in a direction for said first or second sealing member to pressure contact said first or second seat to prevent loss of pressurized air from said interior confined space, but said movement of said valve member being delayed until air in said first or second confined space has been bled through said passage means.

2. A safety device as defined in claim 1 in which said first and second bores are tapped and said first and second plugs are exteriorly threaded and removably engage said tapped bores, and said device in addition including:

h. first and second resilient sealing rings mounted on said first and second plungers that sealingly engage the surfaces of said body defining said first and second cavities.

3. A safety device as defined in claim 1 in which said valve member has recessed ends, and said first and second resilient sealing members being in the form of flat washers that are mounted on said recessed ends.

4. A safety device as defined in claim 3 in which said valve seats have serrations defined thereon that seal with said resilient sealing members when one of said sealing members exerts a force on one of said valve seats.

5. A safety device as defined in claim 1 which in addition includes:

k. a normally open electrical switch mounted on said body, said switch having first and second terminals projecting outwardly therefrom; and

l. fourth means for closing said switch to complete a circuit between said first and second terminals to actuate an electric alarm when said valve member moves to a position where said valve member obstructs the flow of air through said first or second bores.

6. A safety device as defined in claim 5 in which said switch is pressure actuated and said fourth means is a spring loaded check valve that is normally closed but is moved to an open position by said valve member when said valve member moves to a position to obstruct the flow of pressurized air through said first or second bores.

7. A safety device asdefined in claim 1 in which saidvalve member has first and second ends that have first and second cavities extending inwardly therefrom, with said cavities on their adjacent ends connected to small diameter passage means in said valve member through which air from said cavities can bleed, and said second means being first and second 

1. In combination with a pressurized air supply line and first and second air actuated brake assemblies having first and second conduits extending therefrom, a safety device for permitting one of said assemblies to operate when the other thereof has become inoperative by a leak developing therein or in said conduit extending therefrom, said device including: a. a valve body that defines an interior confined space and first and second axially aligned bores in communication therewith, and a third bore normally disposed to said first and second bores and in communication with said interior confined space, said body including a portion thereof in said interior confined space between said first and second bores, and said portion having a fourth bore therein that is longitudinally aligned with said first and second bores; b. first and second plugs mounted in said first and second bores, each of said plugs having a bore and counterbore therein that define a body shoulder at the junction thereof, and said plugs having circular valve seats on the ends thereof disposed in said housing; c. first and second apertured plates disposed in said first and second bores and in abutting contact with said body shoulders; d. first and second plungers that are axially aligned and extend towards one another from said plates; e. a single elongate valve member slidably mounted in said fourth bore, said valve member having first and second end surfaces from which first and second cavities extend inwardly towards one another, with said first and second cavities slidably and sealingly engaged by said first and second plungers that cooperate therewith to define first and second confined spaces that are connected to small diameter passage means in said valve body through which air in said first and second confined spaces is bled to the exterior of said valve member; f. spring means that at all times tend to maintain said valve member in a centered position between said first and second plugs; g. first and second resilient sealing members mounted on said first and second ends of said valve member; h. first means for controlling said pressurized air through said supply line; i. second means for connecting said supply line to said third bore; j. third meanS connecting said first and second conduits to said bores and counterbores in said first and second plugs, said spring means so long as there is no substantial leak in one of said brake assemblies or in said first and second conduits maintaining said valve member in a centered position in said interior confined space where pressurized air can flow from said supply line to said conduits, but upon a leak developing in one of said conduits or brake assemblies an unbalanced pressure develops in said interior confined space that forces said valve member to move in a direction for said first or second sealing member to pressure contact said first or second seat to prevent loss of pressurized air from said interior confined space, but said movement of said valve member being delayed until air in said first or second confined space has been bled through said passage means.
 2. A safety device as defined in claim 1 in which said first and second bores are tapped and said first and second plugs are exteriorly threaded and removably engage said tapped bores, and said device in addition including: h. first and second resilient sealing rings mounted on said first and second plungers that sealingly engage the surfaces of said body defining said first and second cavities.
 3. A safety device as defined in claim 1 in which said valve member has recessed ends, and said first and second resilient sealing members being in the form of flat washers that are mounted on said recessed ends.
 4. A safety device as defined in claim 3 in which said valve seats have serrations defined thereon that seal with said resilient sealing members when one of said sealing members exerts a force on one of said valve seats.
 5. A safety device as defined in claim 1 which in addition includes: k. a normally open electrical switch mounted on said body, said switch having first and second terminals projecting outwardly therefrom; and l. fourth means for closing said switch to complete a circuit between said first and second terminals to actuate an electric alarm when said valve member moves to a position where said valve member obstructs the flow of air through said first or second bores.
 6. A safety device as defined in claim 5 in which said switch is pressure actuated and said fourth means is a spring loaded check valve that is normally closed but is moved to an open position by said valve member when said valve member moves to a position to obstruct the flow of pressurized air through said first or second bores.
 7. A safety device as defined in claim 1 in which said valve member has first and second ends that have first and second cavities extending inwardly therefrom, with said cavities on their adjacent ends connected to small diameter passage means in said valve member through which air from said cavities can bleed, and said second means being first and second plungers that occupy fixed aligned positions in said valve body and slidably and sealingly engage said cavities, with the air in one of said cavities being compressed when the valve member moves relative to one of said plungers in a direction to decrease the volume of said cavity, and the time delay being that required for said compressed air to escape through said passage means. 